This invention relates to a jet propelled watercraft and more particularly to an improved arrangement for positioning the jet propulsion unit in a watercraft hull, for employing multiple jet propulsion units and for treating the exhaust gases from the powering internal combustion engine.
There are a number of advantages to the use of so called water jet propulsion units for propelling watercraft. Unlike conventional propeller powered watercraft, a jet propelled watercraft can operate in much shallower bodies of water. In addition, there are a number of other advantages to the use of jet propulsion units. However, it has been proposed to improve the appearance of the watercraft by positioning the jet propulsion unit at least in part in a tunnel formed in the underside of the hull of the watercraft. This gives a very neat appearance and also permits good balance of the watercraft as opposed to transom mounted jet propulsion units.
Where, however, the jet propulsion unit is mounted within the hull of the watercraft there are certain problems which can arise. In the first instance, because of the fact that jet propelled watercraft can operate in shallow bodies of water, frequently the water inlet to the jet propulsion unit may be clogged and it is desirable to access the water inlet so that it can easily be cleared. Of course, this problem is particularly difficult in connection with watercrafts wherein the jet propulsion unit is mounted in a tunnel in the hull of the watercraft.
In addition, during the periods of time when the jet propulsion unit is not employed to power the watercraft or the watercraft is stationery, encrustation of the water inlet and internal components of the jet propulsion unit can be a problem. To avoid the aforenoted problems it has been proposed to provide a watercraft with a jet propulsion unit that can be moved so that its water inlet portion can be raised from a lowered in the water position to an elevated out of the water position. In addition to permitting the water to be drained from the water inlet opening and jet propulsion unit when not in use, such arrangements also permit the cleaning of the water inlet portion while the hull is still floating in a body of water. A number of advantageous embodiments of watercraft and jet propulsion units of this type are disclosed in the co-pending application of Noboru KobayaShi, entitled Water Jet Propulsion Unit, Ser. No. 07,735,154, filed Jul. 22, 1991, now issued as U.S. Pat. No. 5,254,023 which application is a continuation of his earlier application Ser. No. 07,489,361, filed Mar. 6, 1990, now abandoned which applications are assigned to the Assignee hereof.
As is noted in said co-pending application, one way in which the jet propulsion unit may be elevated is to support it for pivotal movement about a transversely extending pivot axis which is disposed forwardly of the jet propulsion unit and adjacent the bulkhead which separates the tunnel in which the jet propulsion unit is mounted from the engine compartment of the watercraft hull. Normally this pivot axis is positioned in a forward location so as to permit the use of a universal joint driving connection between the engine output shaft and the impeller shaft of the jet propulsion units so that the unit can be tilted up without disconnecting the drive thereto. Of course, because of the pivotal movement and the relatively long length of the jet propulsion unit, the discharge end of the jet propulsion unit moves upwardly a greater distance than the forward portion of the jet propulsion unit upon such pivotal movement. It has been heretofore the practice to provide a tunnel that has substantially uniform height throughout its length and this means that the tunnel can intrude into the remainder of the watercraft hull.
It is, therefore, a principal object of this invention to provide an improved watercraft hull and jet propulsion unit arrangement wherein the jet propulsion unit is supported for pivotal movement about a transverse axis and yet does not provide an undue intrusion into the interior of the hull.
For a variety of reasons, it is desirable to provide a relatively low transom for the hull of a watercraft. However, when a low transom is provided there are some problems that are encountered when the watercraft is rapidly decelerated from a high speed condition. The wake, particularly around the propulsion unit, can then move forward and overflow the rear of the transom if it is too low.
It is, therefore, a still further object of this invention to provide an improved hull and transom construction for a jet propelled watercraft wherein the rear of the transom is designed so as to prevent water from passing back into the hull during sudden decelerations without adversely effecting the rear view from the watercraft.
As has been previously noted, there are substantial advantageous to positioning the jet propulsion unit of a watercraft in a tunnel positioned on the underside of the watercraft hull. However, if the jet propulsion unit discharge nozzle is also positioned completely within this tunnel, certain problems in connection with interference from the discharge, particularly during steering movement of the discharge nozzle, can be encountered.
It is, therefore, a still further object of this invention to provide an improved jet propelled watercraft wherein the jet propulsion unit is mounted within a tunnel in the hull of the watercraft wherein the mounting arrangement is such that the discharge from the discharge nozzle is not obstructed by the sidewalls of the tunnel.
It is a still further object of this invention to provide an improved hull arrangement for a jet propelled watercraft wherein the discharge from the discharge nozzle of the jet propulsion unit is unobstructed but wherein the hull has side portions that are closely positioned to this discharge nozzle.
In connection with the use of jet propulsion units, it is the normal practice to provide a powering internal combustion engine for driving the jet propulsion unit. As is typical with watercraft practice, the exhaust from the internal combustion engine is discharged back into the body of water in which the watercraft is operating to provide some partial silencing. However, when this is done with a jet propulsion unit the exhaust discharge may actually be released in the tunnel where the jet propulsion unit is positioned. Although this has certain advantages when traveling in a forward direction, if the watercraft is operated in reverse the exhaust gases will tend to collect in the tunnel and not be discharged therefrom. This can cause not only contamination of the hull but other problems.
It is, therefore, a further object of this invention to provide an improved arrangement for discharging the exhaust gases from a jet propelled watercraft in such a way that the exhaust gases can flow freely regardless of whether the watercraft is operating in a forward or reverse drive mode.